On November 15, 1630, German mathematician, astronomer, and astrologer Johannes Kepler died in Regensburg, Germany. He is best known for his laws of planetary motion which influenced Isaac Newton‘s theory of universal gravitation.

Kepler was born in Weil der Stadt, Württemberg on December 27, 1571. His father was a mercenary who left his family when Kepler was five years old. His mother was an herbalist and healer who was tried for witchcraft later in her life. Kepler took an interest in mathematics and astronomy as a child, and these interests stuck with him throughout the rest of his life. In 1589, he received a scholarship to study theology at the University of Tübingen. While attending school, he studied under Michael Maestlin who was an advocate of the Copernican Theory, which stated that the sun was the center of the solar system rather than Earth. Nearly all scholars at this time still believed the rest of the solar system revolved around Earth. Though he had originally intended to be a minister, at the end of his studies, he was offered a position as a mathematics and astronomy teacher at Graz.

While teaching at Graz, Kepler wrote Mysterium Cosmographicum, an outspoken astronomical defense of the Copernican System and heliocentrism. During the Catholic Counter-Reformation, Kepler, who was Lutheran, was forced to leave. He moved to Prague where he began to work with renowned astronomer Tycho Brahe. Brahe had both the most exact measuring instruments and the most exact empiric data of his time, and from this data Kepler discovered that the orbit of Mars was an ellipse. He noted his discoveries in Astronomia Nova, which details his first two laws of planetary motion. This work was also the first time a scientist documented how to form an extremely accurate theory using imperfect data. This is known today as the scientific method.

In 1612, Kepler moved to Linz where he again became a teacher and astrological and astronomical adviser. He published Harmonice Mundi in 1619 in which he explained the astronomical and astrological proportions of the natural world in terms of music. He also explained what would come to be known as the third law of planetary motion.

During his lifetime, Kepler was never famous, but his articulations of the astrological and astronomical world led to many other great scientific discoveries that better allow us to understand the way the universe works. Suffering a fever, he died in Regensburg, Germany on November 15, 1630.

International Astrology Day is observed by astrologers and astrology fanatics worldwide every March 20. It is viewed as the first day of the astrological year (or the Astrological New Year) because it is the day when the Sun enters Aries, the first sign of the zodiac.

What’s your sign? There are 12 signs in the Zodiac. Your sign is designated by your date of birth; you can be an Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, or Pieces. Find out more about the Zodiac and what your particular sign says about you.